Micro-blogging site Twitter has been buzzing with screen grabs from Vodafone's Egyptian customers showing pro-government text messages sent to them in the run-up to the violent clashes in central Cairo that broke out on Wednesday.

Vodafone Group PLC said in a statement that Egyptian authorities had been using the country's emergency laws to script text messages to its customers since the beginning of the unrest. The company said it had no ability to change the content of the messages.

"Vodafone Group has protested to the authorities that the current situation regarding these messages is unacceptable," the statement said. "We have made clear that all messages should be transparent and clearly attributable to the originator."

Vodafone has already come under fire for its role in the Internet blackout that cut Egypt off from the online world for several days. The company said the order to pull the plug on its Egyptian customers could not be ignored as it was legal under local law.

The company noted in its statement that the Egyptian government also has the power to compel other mobile operators, including Egypt's Mobinil and Etisalat, to send pre-scripted text messages.

It was not clear whether those companies were also involved. Vodafone did not immediately return a call seeking comment on the exact nature of the government messages, although Twitter users described them as carrying patriotic messages as well as attacks on "traitors".